High-sensitivity strain sensor based on an asymmetric tapered air microbubble Fabry-Pérot interferometer with an ultrathin wall.

A Fabry-Pérot interferometer (FPI) with an asymmetric tapered structure and air microbubble with an ultrathin wall is designed for high-sensitivity strain measurement. The sensor contains an air microbubble formed by two single-mode fibers (SMF) prepared by fusion splicer arc discharge, and a taper is applied to one side of the air microbubble with a wall thickness of 3.6 µm. In this unique asymmetric structure, the microbubble is more easily deformed under stress, and the strain sensitivity of the sensor is up to 15.89 pm/µÉ› as evidenced by experiments.The temperature sensitivity and cross-sensitivity of the sensor are 1.09 pm/°C and 0.069 µÉ›/°C in the temperature range of 25-200°C, respectively, thus reducing the measurement error arising from temperature variations. The sensor has notable virtues such as high strain sensitivity, low-temperature sensitivity, low-temperature cross-sensitivity, simple and safe process preparation, and low cost. Experiments confirm that the sensor has good stability and repeatability, and it has high commercial potential, especially strain measurements in complex environments.

High-sensitivity dual U-shaped PCF-SPR refractive index sensor for the detection of gas and liquid analytes.

A dual U-shaped photonic crystal fiber (PCF) biochemical sensor based on surface plasmon resonance (SPR) is designed for the simultaneous detection of gas and liquid analytes, and the properties are analyzed by the full vector finite element method (FEM). SPR is excited by placing gold nanowires on the inner surface of the U-shaped device. In this technique, the traditional metal deposition process can be replaced, subsequently reducing the difficulty and complexity of actual production and improving the phase matching between the basic mode and plasmonic modes. To improve the detection properties, the structural parameters of the sensor including the air hole diameter, spacing, gold nanowire diameter, and polishing depth are optimized, and to better evaluate and analyze the sensing properties, the wavelength and amplitude modulation inquiry method is adopted. The results show that the maximum wavelength sensitivity (WS), amplitude sensitivity (AS), minimum resolution (R), and optimal FOM are 35,000 nm/RIU, 438.08R I U -1, 2.86×10-6 R I U, and 165.16R I U -1, respectively. In addition, the sensor can detect analyte RIs between 1.00 and 1.36 for gas and liquid analytes simultaneously. Owing to the simple structure, low cost, and ambient-condition monitoring, the sensor has large potential in a myriad of applications including sewage treatment, food safety, humoral regulation, environmental and biological monitoring, and medical diagnosis.

High FOM PCF-SPR refractive index sensor based on MgF2-Au double-layer films.

A simple twin-core D-shape photonic crystal fiber sensor based on surface plasmon resonance (SPR) is designed for the measurement of refractive indices (RI). The twin-core D-shape structure enhances the SPR effect, and the M g F 2-Au dual-layer film narrows the linewidth in the loss spectrum, consequently improving both the sensitivity and figure of merit (FOM). The properties of the sensor are analyzed by the finite element method. In the RI range of 1.32-1.42, the maximum wavelength sensitivity, FOM, and resolution are 62,000 nm/RIU, 1281R I U -1, and 1.61×10-6, respectively.

Relay Copper-Catalyzed Synthesis of Imidazo[1,5-a]pyridine Scaffolds from Phenylalanine and Halohydrocarbon.

An efficient and straightforward strategy to synthesize imidazo[1,5-a]pyridine compounds from phenylalanine and halohydrocarbon has been successfully developed. The protocol features a relay copper-catalyzed reaction involving intermolecular C-O coupling and intramolecular C-N cyclization, providing an approach to access a diverse range of imidazo[1,5-a]pyridine derivatives with unique aza quaternary carbon centers.

Multi-wavelength unidirectional forward scattering properties of the arrow-shaped gallium phosphide nanoantenna.

An arrow-shaped gallium phosphide nanoantenna exhibits both near-field electric field enhancement and far-field unidirectional scattering, and the interference conditions involve electric and magnetic quadrupoles as well as toroidal dipoles. By using long-wavelength approximation and exact multipole decomposition, the interference conditions required for far-field unidirectional transverse light scattering and backward near-zero scattering at multiple wavelengths are determined. The near-field properties are excellent, as exemplified by large Purcell factors of 4.5×109 for electric dipole source excitation, 464.68 for magnetic dipole source excitation, and 700 V/m for the field enhancement factor. The degree of enhancement of unidirectional scattering is affected by structural parameters such as the angle and thickness of the nanoantenna. The arrow-shaped nanoantenna is an efficient platform to enhance the electric field and achieve high directionality of light scattering. Moreover, the nanostructure enables flexible manipulation of light waves and materials, giving rise to superior near-field and far-field performances, which are of great importance pertaining to the practicability and application potential of optical antennas in applications such as spectroscopy, sensing, displays, and optoelectronic devices.

Anti-resonant fiber with high-resistivity silicon for THz wave transmission.

A novel anti-resonant fiber for low-loss terahertz waveguides is proposed and analyzed. The terahertz fiber uses high-resistivity silicon as the bulk material and nine nested double-layer concentric circular tubes in the cladding to reduce propagation losses. The effects of the geometric parameters on the propagation characteristics are analyzed by the finite element method. The result indicates that an ultra-low total loss of 4.9×10-4 d B/m is achieved at f=1T H z. The low-loss propagation window is 0.48 THz ranging from 0.6 to 1.4 THz. In addition, the influence of mechanical bending on the propagation loss is investigated and the bending loss can be maintained at less than 7.3×10-3 d B/m at f=1T H z even if the bending radius is larger than 60 cm. The properties of this anti-resonant fiber are significantly superior to those of previously reported structures and the fiber thus has large commercial potential.

Surface plasmon resonance sensor composed of micro-nano optical fibers for high-sensitivity refractive index detection.

Spurred by the continuous development of surface plasmon resonance (SPR) technology, optical fiber sensors based on SPR have become a research hotspot. Although single-mode fibers (SMFs) are simple and easy to manufacture, the sensitivity is quite poor. On the other hand, even though photonic crystal fibers (PCFs) and anti-resonant fibers (ARFs) can achieve high-sensitivity detection and the wavelength sensitivity is tens of times that of SMFs, they are complex and difficult to produce. Herein, an SPR refractive index sensor composed of micro-nano optical fibers (MNFs) is designed to detect analytes in the refractive index range between 1.33 and 1.43. Analysis by the finite element method (FEM) reveals that the maximum wavelength sensitivity is 49,000 nm/RIU. The SPR sensor boasting a simple structure, low cost, and high wavelength sensitivity has enormous potential in applications such as chemical analysis, environmental monitoring, and other fields.

Surface plasmon resonance sensor composed of a D-type photonic crystal fiber with a three-layer coating.

A surface plasmon resonance sensor composed of photonic crystal fibers (PCF-SPR) with an A u-T i O 2-A u triple layer is designed for refractive index (RI) sensing and analyzed theoretically by the finite element method. The sensor exhibits enhanced resonance coupling between the core mode and surface plasmon polariton (SPP) mode as well as better sensitivity than the structure with a single gold coating. Furthermore, the A u-T i O 2-A u tri-layer structure narrows the linewidth of the loss spectrum and improves the figure of merit (FOM). In the analyte RI range of 1.30-1.42, the maximum wavelength sensitivity is 20,300 nm/RIU, resolution is 4.93×10-6, amplitude sensitivity is 6427R I U -1, and FOM is 559R I U -1. The results provide insights into the design of high-performance PCF-SPR sensors.

Effects of different cladding materials on orbital angular momentum modes propagating in photonic crystal fibers.

With the development of orbital angular momentum (OAM) photonic crystal fibers (PCFs) for more efficient communication, fiber claddings are important to the performance. In this paper, the influence of S i O 2 and four new optical materials, which are amethyst, SSK2, SF11, and LaSF09, as cladding materials, on the OAM mode characteristics is studied based on a common PCF for OAM transmission. In addition, the effective index difference, dispersion, confinement loss, and other properties of OAM modes transmitted in the five materials are derived by the finite element method. After in-depth analysis, universal rules can be obtained as guidelines for optimization of PCF in the future for improving the efficiency of optical fiber communication. Through chart analysis, it can be concluded that when materials of high effective refractive indices are used as cladding materials for PCF, the dispersion, nonlinear coefficient, confinement loss, mode purity, and other properties are significantly improved. Lower dispersion and confinement loss are more conducive to long-distance communication transmission. The decrease in nonlinear coefficient represents a better effect in suppressing nonlinear effects, and the increase in numerical aperture and mode purity respectively improves the transmission efficiency and stability of OAM communication. These conclusions provide universal rules for high-quality communication in the future.

HE1,1 mode excited surface plasmon resonance for high-sensitivity sensing by photonic crystal fibers.

Surface plasmon resonance (SPR) is widely used in photonic crystal fiber sensors. In this work, a photonic crystal fiber sensor based on HE1,1 mode excited SPR is designed and analyzed by the finite element method. The maximum wavelength sensitivity, optimal resolution, and amplitude sensitivity of the optical fiber sensor are 24,600 nm/RIU, 4.07×10-6RIU, and 1164.13RIU-1, respectively, for the refractive index range between 1.29 and 1.39. The sensor has excellent properties and wide application prospects in bimolecular and biochemical sensing, environmental monitoring, food safety, and other fields.

Design of optical anapole modes of all-dielectric nanoantennas for SERS applications.

To obtain large electric field enhancement while mitigating material losses, an all-dielectric nanoantenna composed of a heptamer and nanocubes is designed and analyzed. A numerical simulation by the finite element method reveals that the nanoantenna achieves the optical electric anapole modes, thereby significantly enhancing the coupling between different dielectrics to further improve the near-field enhancement and spontaneous radiation. Field enhancement factors |E/E 0|2 of 3,563 and 5,395 (AM1 and AM2) and a Purcell factor of 3,872 are observed in the wavelength range between 350 and 800 nm. This nanoantenna has promising potential in applications involving surface-enhanced Raman scattering and nonlinearities due to its low cost and excellent compatibility.

Short dual-core GaAs photonic crystal fiber splitter with a broad bandwidth and ultrahigh extinction ratio.

Microstructured polarization beam splitters (PBSs) have attracted much interest in recent years. Here, a ring double-core photonic crystal fiber (PCB) PSB (PCB-PSB) with an ultrashort, broadband, and high extinction ratio (ER) was designed. The effects of the structural parameters on the properties were analyzed by the finite element method, which revealed that the optimal length of the PSB was 19.08877 µm and the ER was -324.257d B. The operating bandwidth for an ER of less than -20d B is 440 nm, and the wavelength range spans the full E+S+C+L+U band between 1,320 and 1,760 nm. The fault and manufacturing tolerance of the PBS was demonstrated for structural errors of ±1%. Moreover, the influence of temperature on the performance of the PBS was determined and discussed. Our results show that a PBS has excellent potential in optical fiber sensing and optical fiber communications.

Double-ring-disk hybrid nanostructures with slits for electric field enhancement.

Although noble metal nanoantennas have distinctive optical properties and local electric field enhancement, considerable non-radiative ohmic losses occur at the optical frequencies, consequently creating significant absorption and unwanted heating. Combining the plasmon mode of metal nanoantennas with the anapole mode of high refractive index dielectric materials offers a promising alternative to increase the electric field strength with minimal loss. Herein, a silicon disk with slots and two Au rings with a coupling mechanism are described. To elucidate the field enhancement mechanism, the near-field enhancement features and near-field electric field distributions are explored by a numerical simulation and multipole decomposition analysis. By opening the slit to generate high-intensity hot spots inside the disk, the electric field can be enhanced significantly, and nearby molecules can directly contact these hot spots. The resulting large field enhancement suggests significant applications to strong photon-exciton coupling and nonlinear photonics.

UPLC-QE-Orbitrap-Based Cell Metabolomics and Network Pharmacology to Reveal the Mechanism of N-Benzylhexadecanamide Isolated from Maca (Lepidium meyenii Walp.) against Testicular Dysfunction.

Testicular dysfunction (TDF) is characterized by testosterone deficiency and is caused by oxidative stress injury in Leydig cells. A natural fatty amide named N-benzylhexadecanamide (NBH), derived from cruciferous maca, has been shown to promote testosterone production. Our study aims to reveal the anti-TDF effect of NBH and explore its potential mechanism in vitro. This study examined the effects of H2O2 on cell viability and testosterone levels in mouse Leydig cells (TM3) under oxidative stress. In addition, cell metabolomics analysis based on UPLC-Q-Exactive-MS/MS showed that NBH was mainly involved in arginine biosynthesis, aminoacyl-tRNA biosynthesis, phenylalanine, tyrosine and tryptophan biosynthesis, the TCA cycle and other metabolic pathways by affecting 23 differential metabolites, including arginine and phenylalanine. Furthermore, we also performed network pharmacological analysis to observe the key protein targets in NBH treatment. The results showed that its role was to up-regulate ALOX5, down-regulate CYP1A2, and play a role in promoting testicular activity by participating in the steroid hormone biosynthesis pathway. In summary, our study not only provides new insights into the biochemical mechanisms of natural compounds in the treatment of TDF, but also provides a research strategy that integrates cell metabolomics and network pharmacology in order to promote the screening of new drugs for the treatment of TDF.

Highly sensitive dual-core photonic quasicrystal fiber methane sensor based on surface plasmon resonance.

A highly sensitive dual-core photonic quasicrystal fiber methane sensor based on surface plasmon resonance is designed and analyzed. In this sensor, cryptophane E is doped with polysiloxane and Ag and used as the sensitive film and plasma medium, respectively, for sensitive detection of methane. The influence of the structural parameters on the sensor properties is analyzed by the finite element method. The optimized dual-quasi-D-shape structure has excellent methane-sensing properties such as maximum and average wavelength sensitivities of 14 and 10.98 nm/%, respectively, in the methane concentration range of 0%-3.5%. The sensitivity is better than that of similar sensors reported previously.

Electric field enhancement by a hybrid dielectric-metal nanoantenna with a toroidal dipole contribution.

Plasmonic nanocavities enable extreme light-matter interactions by pushing light down to the nanoscale. The numerical simulation is carried out systematically on the slotted Φ-shaped Si disk system with the super-dipole mode based on the analysis of the scattering strength of electric and toroidal dipoles. New blocks are introduced to the zero-field strength region of a slotted Si disk system as a function of the field enhancement factors. The far-field scattering characteristics and near-field electromagnetic field distributions are investigated by a multipole decomposition analysis to elucidate the intrinsic causes of the field enhancement. In the hybrid metal-dielectric nanoantenna, the Φ-shaped Si structure is prepared by superimposing Au nanoantennas for further field enhancement. In addition, the effects of the placement of an electric dipole emitter on the Purcell factor are derived. The geometric volume of the system is increased, and the electric field strength is improved, leading to an electric field increase of ∼30. Coupling between the super-dipole mode of the dielectric nanostructure and plasmonic modes of the metallic nanoantenna produces an enhancement as large as 16 times. Our results reveal a greatly enhanced super-dipole mode by electromagnetic coupling in composite structures, which will play a significant role in enhanced nonlinear photonics, near-field enhancement spectroscopy, and strong photon-exciton coupling.

Tenuifolin ameliorates chronic restraint stress-induced cognitive impairment in C57BL/6J mice.

The general consensus is that stress affects the central nervous system and can lead to cognitive problems. The root of Polygala tenuifolia (P. tenuifolia) is a well-known traditional Chinese medicine used for improving brain function. Tenuifolin (TEN) is the major constituent of P. tenuifolia and has a promising neuroprotective property. The purpose of this study was to investigate the alleviating effect of TEN on cognitive impairment induced by chronic restraint stress (CRS) and its mechanism. Our results showed that CRS exposure resulted in impaired cognitive performance in C57BL/6J mice, as indicated by decreased responses in Y-maze, novel objects recognition, and step-through passive avoidance tests. TEN treated daily orally (10 and 20 mg/kg) for 30 days reversed these behavior changes. Meanwhile, TEN could significantly regulate interleukin (IL)-6 and IL-10 levels in the hippocampus. TEN inhibited the toll-like receptor 4/nuclear factor-kappa B-mediated inflammation, as well as adrenocorticotropic hormone and corticosterone levels in serum. Most importantly, we found that TEN also upregulated the expressions of brain-derived neurotrophic factor, tropomyosin kinase B, glucocorticoid receptor, glutamate receptor 1, and synapse-associated proteins. Collectively, these data suggest that TEN has a potential improvement effect on memory loss caused by CRS.

Screening of the Active Compounds against Neural Oxidative Damage from Ginseng Phloem Using UPLC-Q-Exactive-MS/MS Coupled with the Content-Effect Weighted Method.

The neuroprotective properties of ginsenosides have been found to reverse the neurological damage caused by oxidation in many neurodegenerative diseases. However, the distribution of ginsenosides in different tissues of the main root, which was regarded as the primary medicinal portion in clinical practice was different, the specific parts and specific components against neural oxidative damage were not clear. The present study aims to screen and determine the potential compounds in different parts of the main root in ginseng. Comparison of the protective effects in the main root, phloem and xylem of ginseng on hydrogen peroxide-induced cell death of SH-SY5Y neurons was investigated. UPLC-Q-Exactive-MS/MS was used to quickly and comprehensively characterize the chemical compositions of the active parts. Network pharmacology combined with a molecular docking approach was employed to virtually screen for disease-related targets and potential active compounds. By comparing the changes before and after Content-Effect weighting, the compounds with stronger anti-nerve oxidative damage activity were screened out more accurately. Finally, the activity of the selected monomer components was verified. The results suggested that the phloem of ginseng was the most effective part. There were 19 effective compounds and 14 core targets, and enriched signaling pathway and biological functions were predicted. After Content-Effect weighting, compounds Ginsenosides F1, Ginsenosides Rf, Ginsenosides Rg1 and Ginsenosides Rd were screened out as potential active compounds against neural oxidative damage. The activity verification study indicated that all four predicted ginsenosides were effective in protecting SH-SY5Y cells from oxidative injury. The four compounds can be further investigated as potential lead compounds for neurodegenerative diseases. This also provides a combined virtual and practical method for the simple and rapid screening of active ingredients in natural products.

High-sensitivity methane sensor composed of photonic quasi-crystal fiber based on surface plasmon resonance.

A photonic quasi-crystal fiber (PQF) methane sensor based on surface plasmon resonance (SPR) is designed and described. The double-side polished six-fold photonic quasi-crystal fiber coated with a silver film produces enhanced SPR effects and sensitivity. A nanostructured thin film with cryptophane-E-doped polysiloxane is deposited on silver as the methane-sensitive surface layer and to mitigate oxidation of silver. The sensor is analyzed and optimized numerically by the full-vector finite element method. For methane concentrations in the range of 0% to 3.5%, the maximum sensitivity of the sensor is 8 nm/%, and the average sensitivity is 6.643 nm/%. Compared to traditional gas sensors, this sensor provides accurate sensing of methane besides offering advantages such as the low cost, miniaturized size, online monitoring, and immunity to electromagnetic field interference.

Surface plasmon resonance sensor based on U-shaped photonic quasi-crystal fiber.

A high-sensitivity surface plasmon resonance (SPR) sensor is designed and analyzed numerically. The sensor is constructed on the eightfold U-shaped photonic quasi-crystal fiber (PQF) and coated with indium tin oxide (ITO). The coupling between the core mode and surface plasmon polariton mode is enhanced due to shortening of the distance between the core and the ITO layer, so that the PQF-SPR sensor exhibits high refractive index (RI) sensitivity in the near-infrared region. The maximum wavelength sensitivity and the corresponding resolution of this sensor are 42,000 nm/RIU and 2.38×10-6RIU, respectively. The average wavelength sensitivity is 12,750 nm/RIU in the refractive index range of 1.306-1.386. This advanced sensor is suitable for the determination of RIs in the near-infrared region.